This invention is described in Disclosure Document No. 126,933 filed Apr. 27, 1984, in the U.S. Patent and Trademark Office.
The present invention pertains to the loudspeaker system art and, more particularly, to loudspeaker systems including frequency shaping equalizer circuits.
Conventional loudspeaker systems employ an enclosure that houses one or more speakers, or drivers. The drivers are typically mounted in openings provided through the front baffle of the enclosure, such that front wave radiation from the speaker radiates into the listening area, whereas backwave energy is radiated within the enclosure.
A problem encountered by designers of loudspeaker systems has been that the response of a typical driver is linear only over a limited bandwidth. Thus, to provide a relatively flat frequency response over the entire audio bandwidth (i.e., 20-20, 000 Hz) multiple drivers have been employed in high quality loudspeaker systems, with each of the multiple drivers specifically designed to cover a selected portion of the audio bandwidth. In a two-way system, for example, a low-frequency driver, or woofer, is employed for low frequencies and a high-frequency driver, or tweeter, is used for high frequencies.
To assure a smooth response over the audio bandwidth, loudspeaker system designers have utilized crossover networks in an attempt to produce a "seamless" overall system response for signals that occur within the crossover points of multiple drivers. The function of the crossover network in a two-way system is to divide the input signal from the amplifier into low-frequency signals which are routed to the woofer and high-frequency signals which are routed to the tweeter. The high-frequency response of the woofer is rolled off in a controlled manner, with the tweeter's low-frequency response rolled off in a complementary manner such that as constant amplitude signals of varying frequency are applied to the overall system, a linear frequency response is obtained even at the crossover frequency.
In most conventional loudspeaker systems, bass response is augmented by resonance of the low frequency driver and the enclosure. Upon the loudspeaker being driven by a signal at, or near, this resonant frequency, a resonant mode is excited and the loudspeaker system "rings," producing a corresponding output. Whereas some listeners are initially deceived by this ringing believing it to be a bass enhancement, in fact such ringing constitutes a distortion which obscures the clarity of the sound being reproduced, ultimately leading to listener fatigue and dissatisfaction with the loudspeaker system.